The lone voice of Rachel Carson warning of impending environmental disaster has been joined over the last 25 years by a ground swell of concern about the effects of man’s activities on our planet. Key among the issues concerning environmentalists and regulators are the health and ecological effects of toxic chemicals being released into the environment. Unfortunately, assessing either exposure to or effects of environmental contaminants is fraught with uncertainties. There are a number of difficulties in estimating the extent of exposure to toxic chemicals in the environment, and even greater difficulty in attributing, let alone predicting, the adverse health or ecological effects that result from the exposure.